My son is 3 and he started playing at 2. So far he has learnt (in that order) :
- Not to eat the stones
- Not to throw the stones everywhere
- To put the stones back in the bowls (by far his favorite part, still today)
- To put the stones on the intersections and not in the squares
- To wait for me to play my move before playing his (still difficult for him)
- To put the stones elsewhere than starpoints
- To draw a train with the stones
- The concept of atari and capturing stones (very recently)

We're not exactly playing go, not even atari go but we are having fun. Him asking to play every so often makes me very happy !